Pictured above: long-span racking set against a wall in a small store, from our project archive (B3). The wall looks like free support and the strip behind the bays looks like nothing at all. Both are decisions, and this article is about making them on purpose.

Every racking layout answers the same question early, usually without anyone saying it out loud: which runs go against the walls, and which stand back-to-back in the middle of the floor? It then quietly decides how many aisles the warehouse needs, what the fire-safety design has to allow for, what the landlord will let you drill, and whether anyone can clean or inspect behind the steel for years.

Here is how we think about it at the survey, and what to check before a layout drawing gets anywhere near a quotation.

The arithmetic: an aisle should serve two faces

An aisle is the most expensive strip of floor in a racked warehouse, because it stores nothing. Its width is set by the truck, not by you. On our pallet racking systems page we publish the ranges we design to: counterbalance forklifts need aisles of about 3.5 to 4.0 metres, reach trucks 2.4 to 2.8 metres, and VNA trucks 1.6 to 1.8 metres with a flat-floor survey. How we arrive at the working figure for a specific truck is in forklift turning radius and aisle width.

Whatever the width, an aisle costs the same floor whether it has racking on one side or on both. So the layout that uses a floor well is the one where every aisle has a rack face on each side. In a typical rectangular unit that pattern looks like this, running across the floor:

• a single-sided run against one wall,
• an aisle,
• a back-to-back pair,
• an aisle,
• another back-to-back pair, as many as the width allows,
• an aisle,
• a single-sided run against the opposite wall.

Seen that way, the wall runs are not the problem and not a bonus either. They are the other face for the outermost aisles. What wastes a floor is an aisle with racking on one side only — typically a back-to-back pair that did not fit, so one row got dropped and its aisle stayed. When a layout's pallet count looks low for the floor area, that is the first thing we look for. The wider question of what a floor really holds is in how many pallet positions a warehouse actually gets.

What a back-to-back run actually is

A back-to-back run is two rows of frames standing behind each other, joined by row spacers bolted between the uprights. The spacers hold the two rows at a fixed distance and make the pair behave as one structure rather than two rows that happen to be close together.

The gap between the two rows is the flue space, and it is not spare storage. In a sprinklered building it is part of how the fire protection is meant to work, so its width comes from the fire-safety design for your building and your goods, not from the racking drawing and not from a rule of thumb off an overseas website. Our note on SCDF sprinkler clearance and racking approval covers how the racking and the sprinkler design get settled together.

Two things eat that gap on a working floor, and neither shows up on a drawing:

• Pallets deeper than the frame. A load that overhangs at the back consumes the flue from both sides at once. The same pallet that fits "near enough" on a 1200×1000 mm frame design becomes a problem when a customer starts shipping on something longer — see non-standard pallet sizes.
• Pallets pushed too far back. A driver who places each pallet until it stops is using the pallet on the other side as the stop. Over a year, the flue closes one placement at a time.

Against the wall: what the floor plan does not show

On a floor plan a wall is a clean line. At the survey it is almost never clean. Before a run is drawn against any wall, we walk its full length and note what is on it, because each of these either moves a bay or ends a run:

• Doors, including the ones nobody uses. A side door that stays locked is often still an exit. Building a run across an exit is the classic reason a layout gets sent back — escape routes in a racked warehouse explains why the racking always loses that argument.
• Fire equipment. Hose reels, extinguishers, alarm call points and hydrant valves have to stay visible and reachable. A bay in front of one is a bay that gets taken out.
• Electrical boards, isolators and switches. Someone will need to reach the distribution board in a hurry one day. It cannot be behind two tonnes of stock.
• Roller shutter guides and their motors, downpipes, louvres, windows and wall-mounted equipment. Each one sets where a bay can start or stop, or how high the top beam can go at that point.
• Building columns along the wall line. They rarely fall where a bay ends. How we lay runs around them is in columns and obstructions in a racking layout.

None of these is unusual. They get missed when a layout is drawn from the tenancy plan instead of the floor.

The strip behind a wall run

The decision people skip is the gap between the back of a wall run and the wall. Push the frames hard against the wall and you are left with a few centimetres nobody can see into, clean, or inspect. That strip collects dropped cartons, shrink-wrap, dust and, in a food operation, pests. It also hides the back of every upright in the run, which is exactly the face an inspector needs to see. What an inspection looks at is set out in what a rack inspection flags.

The honest options are two: close the gap properly so there is no void, or leave a real gap that a person can get into. The width that works depends on your building and how you clean — in a food warehouse it is set by the cleaning and pest-control regime, as we cover in racking in a food warehouse. The one option that never works is the in-between.

One more thing about that strip: the wall is not a pallet stop. A pallet pushed back until it hits the wall is putting a load into something that was never designed to take it, and on many units that wall is a cladding panel.

"Can we just fix the racking to the wall?"

It is one of the most common questions we get, and the answer is that it is a design decision, made with two facts known: what the wall is built of, and who owns it.

Pallet racking is designed to stand on its own base plates and floor anchors. Racking has to be anchored — that part is not optional. Whether it is also tied back to a wall depends on the wall. A solid internal wall in a small store is a different thing from a precast panel, blockwork infill, or metal cladding on a steel frame, and many warehouse walls are the latter. A wall that was never designed to take a horizontal load from a loaded rack should not be asked to.

Then there is ownership. In a leased unit, the wall is the landlord's, just as the floor is. Drilling it is an alteration to his building, it may need written consent, and every fixing is a hole to make good at the end of the lease. Our article on racking in a leased warehouse covers the consent and reinstatement clauses that decide this; the wall is simply one more thing on that list.

For the record, on the light-duty store pictured above, the shelving was fixed back to the wall with brackets. That was a small room with solid internal walls and hand-loaded shelves. It is not a template for a pallet run in a leased industrial unit.

Single-sided runs and height

A single-sided run is one frame deep. A back-to-back pair joined by row spacers acts as a deeper structure. That difference matters more as runs get taller, and it is one of the things that gets checked in the design rather than judged by eye on the day — which is also why a PE-stamped calculation comes into play on taller or unusual installations. If a layout calls for a tall, standalone single-sided run with nothing beside it, expect that run to be looked at more closely than the rest of the drawing.

The same logic applies to the idea of using racking as a partition. A back-to-back run down the middle of a unit reads like a neat boundary on a plan, but a racking run is not a wall — see subletting part of your warehouse for why.

Run ends take the hits

Back-to-back pairs create run ends facing the cross aisles, and those ends are where forklifts turn. The end frame of a run is the upright most likely to be struck. Wall runs have fewer exposed ends, but the end nearest a doorway or a turn takes the same punishment. Protection belongs in the layout, not added after the first dent — see rack protection, column guards and barriers.

Before the layout is drawn: a checklist

• Which truck, and therefore which aisle width? Every aisle should have a rack face on both sides.
• Walk every wall. List doors, fire equipment, electrical boards, shutters, downpipes, louvres and columns, with positions.
• Ask what the fire-safety design needs between back-to-back rows and above the top load — before the frame depths are chosen.
• Check your pallets against the frame depth, including the longest one a customer might send.
• Decide the strip behind each wall run: closed, or a real gap. Never a few centimetres.
• In a leased unit, get written answers on drilling the floor and fixing to walls before installation is scheduled.
• Mark the run ends that face turning traffic, and plan the protection with the layout.

The short version

Aisles with racking on one side only are what waste a floor. The gap between back-to-back rows belongs to the fire design. Whether racking is fixed to a wall depends on what it is made of and whose it is. And a floor plan will not tell you where the hose reel is.

Planning a layout and want the wall runs and back-to-back pairs settled properly? WhatsApp us on 9107 2601 and we will walk the walls at the site survey before we draw a single bay. Our systems are on the pallet racking systems page and the full scope is on services.

Related reading: forklift turning radius and aisle width · escape routes in a racked warehouse · racking in a leased warehouse